For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips.
The core patterning process in substrate manufacturing is approaching a fundamental limit in line/space resolution capability based on conventional technologies. Novel technologies are needed to break through these technological barriers and enable the substrate manufacturing of upcoming technology nodes. The core patterning step in the manufacturing of substrates typically utilizes a wet etch process, which comprises an impinging liquid spray of a copper etchant through a pressurized nozzle orifice onto predefined exposed copper regions bounded by a dry film resist (DFR) defined by a photolithographic step.
Traditionally, the field has focused on etching solutions based on either acidic etching (Cupric Chloride in hydrochloric acid) or alkaline etching (cupric chloride complexed with ammonia) for which, under conventional spray conditions, the etching process tends to be isotropic. Isotropic etching presents a fundamental limitation in the etch resolution capability as the etch depth is equal to the etch undercut for a perfectly isotropic case.
Preferential downward (anisotropic) etching is capable of achieving smaller space resolution than isotropic etching and can accommodate tighter core patterning design rules. Preferential downward etching is possible utilizing conventional technologies by implementing hydrodynamic conditions which promote non-uniform stirring along the surface resulting in non-uniform etching. This is achieved through judicious control of convective transport processes by tuning the DFR bias (e.g., DFR thickness and space aspect ratio), process dwell time (i.e., processing time), spray characteristics of the liquid etchant, and bath conditions (chemical concentrations, bath temperature, etc.) which under certain conditions create directionality to the etching process. This approach, however, is limited and alternative approaches need to be explored to improve etch resolution capability and meet upcoming design rules.
In addition, due to the limitations of current etching techniques 3, a critical dimension (CD) of the DFR must be made larger than the CD of metal features to compensate for undercuting that occurs beneath the DFR. A so called patterning bias must be used to compensate for the undercut and achieve the desired design feature size. The DFR thickness and space aspect ratio plays a key role in the flow dynamics inside the cavity, which significantly impact the etch resolution capability.
Thus, novel technologies that drive improvements in the subtractive etch resolution capability will be needed to enable the manufacturing of future technology nodes. Technologies are needed that enable preferential anisotropic etching that suppresses undercutting that occurs during metal etching.